How to tell if someone in your family is bipolar or has multiple personalities?

If you have someone in your family who is like hot and cold, one minute they are smiling and the next minute cursing you out, does that mean that they are bipolar or has multiple personalities, and how do they get that way?

That is a good sign of bipolar disorder. Mamy mental illnesses have a genetic predisposition, and then stress may trigger a full-blown episode. Multiple personalities are actually pretty rare; usually are a result of severe child abuse, a way for the child to escape their horrible reality. The problem with mentally ill family member is that it is almost impossible to get them into treatment if they don't want to go! I have a family member who is schizophrenic so I am speaking from experience. Here is a link to an article I wrote, it is about dealing with a family member who is schizophrenic, but the two conditions have some similarities, so it may be of help to you:
http://www.associatedcontent.com/article/170735/the_family_and_schizophrenia.html